Abstract
Late blight, caused by the oomycete Phytophthora infestans, is the most devastating disease in potato-producing regions of the world. Cultivation of resistant varieties is the most effective and environmentally friendly way to control potato late blight disease, and identification of germplasms with late blight resistance and clarification their genetic relationship would promote the development of the resistant varieties. In this study, a diverse population of 189 genotypes with potential late blight resistance, consisting of 20 wild species and cultivated Solanum tuberosum Andigenum group and Chilotanum group, was screened for the presence of late blight resistance by performing challenge inoculation with four Phytophthora infestans isolates including one 13_A2 isolate, CN152. Ten elite resources with broad-spectrum resistance and 127 with isolate-specific resistance against P. infestans were identified. To improve the available gene pool for future potato breeding programs, the population was genotyped using 30 simple sequence repeat (SSR) markers covering the entire potato genome. A total of 173 alleles were detected with an average of 5.77 alleles per locus. Structure analysis discriminated the 189 potato genotypes into five populations based on taxonomic classification and genetic origin with some deviations. There was no obvious clustering by country of origin, ploidy level, EBN (endosperm balance number) value, or nuclear clade. Analysis of molecular variance showed 10.08% genetic variation existed among populations. The genetic differentiation (Fst) ranged from 0.0937 to 0.1764, and the nucleotide diversity (π) was 0.2269 across populations with the range from 0.1942 to 0.2489. Further genotyping of 20K SNP array confirmed the classification of SSRs and could uncover the genetic relationships of Solanum germplasms. Our results indicate that there exits abundant genetic variation in wild and cultivated potato germplasms, while the cultivated S. tuberosum Chilotanum group has lower genetic diversity. The phenotypic and genetic information obtained in this study provide a useful guide for hybrid combination and resistance introgression from wild gene pool into cultivated species for cultivar improvement, as well as for germplasm conservation efforts and resistance gene mining.
Highlights
Potato (Solanum tuberosum) is the most important non-cereal crop plant and ranks third in world food production (Lenman et al, 2016)
Screening of 189 wild and cultivated genotypes for resistance to the P. infestans isolates 80029, T30-4, 90128, and CN152, which are of different complexity and exhibit different levels
The potato research group at IVF, CAAS maintains a collection of 3,000 potato accessions, from which breeders can choose germplasm for resistance evaluation
Summary
Potato (Solanum tuberosum) is the most important non-cereal crop plant and ranks third in world food production (Lenman et al, 2016). The prevalent and widespread outbreaks of the devastating late blight (LB) disease, which is caused by the oomycete Phytophthora infestans, have long posed a threat to global potato production and food safety (Armstrong et al, 2018). The European LB population, which is derived from new isolates, including the A2 mating type, from Mexico that spread to Europe beginning in 1984, is capable of sexual reproduction and, because of this, may potentially evolve the ability to overcome resistance (R) genes in cultivated potato (Goodwin and Drenth, 1997). All 11 R genes (R1-R11) conferring race-specific resistance derived from Solanum demissum, which was extensively used in breeding for LB resistance in potato, have been overcome (Foster et al, 2009). There is a need to identify new resistance germplasms and R genes (Foster et al, 2009)
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